Supreme Court Justice David Souter has long said that he wanted to leave the court and Washington. An intensely private native of small town New Hampshire, he has never warmed to the nation's capital, socializing infrequently and focusing his energies on work and jogging after hours. While he has told many that he would stay on "for the duration," most understood that to mean the tenure of Republican control in the White House. With Obama's victory last November, Souter's long "duration" was over.

And now that Souter has made the decision to leave the court when it finishes its term in June, Washington will turn its attention to whom Obama might nominate to replace him. Souter's reliably liberal stand on issues means that the President's choice won't change the balance of the court on any of the high-profile social issues it handles, like abortion, civil rights or the death penalty. But it does present the President with both political opportunities and challenges, as well as a test of what is thought to be his center-left judicial outlook.

Obama has had some time to consider his choices. The recent health problems of Justice Ruth Bader Ginsburg, who was diagnosed with pancreatic cancer but following surgery in February has returned to the court, already had the White House thinking; indeed, some observers believe that Ginsburg's problems may have delayed Souter's decision, since justices try not to retire at the same time, to allow for an orderly nomination and confirmation process.

Souter himself hadn't hidden from the new Administration his desire to leave. Outsiders had picked up indications: though Souter has always been the last of his colleagues to choose his clerks for the next term, court watchers had focused with increasing interest on the fact that Souter, alone among the justices, still not yet finalized his picks as of late April.

So who will get his job? There is near consensus among sources inside and outside the Administration that the President will pick a woman. George W. Bush replaced one of the court's two women, Sandra Day O'Connor with a man, Justice Samuel Alito, after Bush's legal counsel, Harriet Miers, withdrew under attack from the right. The other near-absolute requirement will be relative youth, as Obama and the Democrats will want to ensure a left-of-center voice for decades to come on a court featuring two relatively young conservative justices, Alito and Chief Justice John Roberts. (See pictures of John Roberts.)

Elena Kagan, 49, the Administration's current Solicitor General and the former dean of Harvard Law School, is considered a front-runner. Politically savvy and well-liked as dean, she met Obama when she was at the University of Chicago Law School in the 1990s. Respected by conservatives, she is popular at the White House. On the downside, she has no judicial or prosecutorial experience and has only served a little over a month as Solicitor General; Obama may want to leave her there for a while.

Another person who will be seriously considered is Diane Wood of the Seventh Circuit court of appeals in Chicago. A very smart and hard-working liberal, Wood knows Obama, though not well, and is the most respected judge among the likely candidates. She has a few knocks against her, though. At 59, she may be older than Obama and the Democrats would like. And she's from Obama's adopted hometown of Chicago, which means her nomination could appear politically provincial.

Sonia Sotomayor, 55, of the Second Circuit court of appeals is a strong candidate for a number of reasons. A relative centrist from the Bronx, New York, she is 55 and has a 12-year, highly respected and largely uncontroversial record as a judge. If Obama chose her she would become the first Hispanic justice on the Supreme Court. That's no small consideration. As their numbers have grown in the U.S., Hispanics have become a key target of political competition between the Democrats and Republicans, and many in the community believe it is time for them to be represented on the nation's highest court. Republicans briefly made gains with them under Bush, but have lost ground recently; amid the battle over immigration reform, a majority of Hispanics backed Obama in the 2008 election. Naming Sotomayor would be a particularly big blow to the GOP, which has suffered a string of them lately.

The one non-judicial candidate considered to be in the top tier of potential choices is Jennifer Granholm, 50, the current governor of Michigan. With a court full of Circuit judges, Granholm would make a mark as a politician, a throwback to the past when politicians, like Earl Warren or Hugo Black, were often chosen for the Supreme Court. And there could be political reasons for picking her; though he won it quite handily, Michigan is still a swing state, and Granholm would please unions, one of several groups Obama will have to contend with on his left. Labor and some civil rights groups have long complained that some Clinton appointees, especially Justice Stephen Breyer, are too centrist on business or national security issues, and they will pressure Obama for a reliably liberal voice.

No nomination to the Supreme Court is free of political fighting, but Republicans will have a hard time landing punches under the circumstances. Already unpopular, especially compared with Obama's soaring numbers, the GOP is in a weak position to oppose the President. Bush's two picks for the Supreme Court were well to the right, but were respected jurists and made it through largely unscathed; Sotomayor, Wood and Kagan would be expected to do the same, though Granholm, as a politician, might have a tougher time. Vetting will be thorough for any candidate, but the four front-runners have long, well-known records: the two judges from their time on the bench, Kagan thanks to her confirmation process for Solicitor General and Granholm as a candidate for statewide office in Michigan. In the unlikely event of a filibuster (Supreme Court nominees are rarely blocked in that way), Obama is also in a position of strength thanks to this week's defection of Senator Arlen Specter.